The invention is based on a fuel injection valve for internal combustion engine.
DE has disclosed a fuel injection valve which contains a valve member that is supported so that the valve member can move bidirectionally, wherein a fuel outlet opening can be controlled with the valve member. In the known fuel injection valve, the valve member has a first opening surface, which defines a first opening pressure chamber in the opening direction of the valve member. The first opening pressure chamber is connected to a high-pressure fuel source and wherein the pressure in the first opening pressure chamber produces a first opening force against the first opening surface. In addition, the valve member has a first closing surface, which defines a first closing pressure chamber in the closing direction of the valve member. The first closing pressure chamber is connected to the high-pressure fuel source and wherein the pressure in the first closing pressure chamber produces a first closing force against the first closing surface.
In the known fuel injection valve, the connection of the first closing pressure chamber to the high-pressure fuel source is produced by means of a throttle location. In addition, the first closing pressure chamber communicates with a discharge chamber that is connected to a relatively pressure-free reservoir. The connection of the first closing pressure chamber to the relatively pressure-free discharge chamber can be switched open and closed with a control valve. When an injection event is to be executed, i.e. when the valve member is to be actuated, the control valve is actuated to open the connection between the first closing pressure chamber and the discharge pressure chamber. Since more fuel flows out of the first closing pressure chamber into the discharge pressure chamber when the control valve is open than can flow through the throttled connection with the high-pressure fuel source into the first closing pressure chamber, a pressure drop occurs in the first closing pressure chamber. The pressure drop reduces the first closing force. As a result, the first opening force prevails and the valve member is moved axially so that the valve member unblocks the fuel outlet opening. In order to end the injection event, the control valve is actuated to close the connection between the discharge pressure chamber and the first closing pressure chamber. Due to the connection of the first closing pressure chamber to the high-pressure fuel source, the original closing force can be rapidly reinstated against the first closing surface in the first closing pressure chamber so that the valve member closes the fuel outlet opening once more.
In the known fuel injection valve, since relatively small forces, which must be exerted to adjust the control valve, generate relatively large forces against the valve member in order to move the valve member, in fuel injection valves that operate according to this principle, reference is often made to an indirect valve member control or actuation or to a xe2x80x9cservo principlexe2x80x9d.
Although the fuel injection valves operating according to this servo principle have proven themselves in actual use, embodiments are continuously being sought which permit even shorter control times for the fuel injection valve in order to improve the emissions levels, efficiency, and noise generation of the internal combustion engines that are operated using them, in particular diesel engines.
With the fuel injection valve according to the invention, it is now possible to achieve shorter control times for the actuation of the valve member so that smaller fuel injection quantities can be more precisely metered and more precisely defined injection times can be achieved. The invention is based on the general concept of producing, with the aid of the first opening force and the first closing force against the valve member, a quasi-static force equilibrium which is essentially maintained even during the adjusting movements of the valve member. The forces required for the adjustment of the valve member are then introduced by the actuating means directly onto the valve member in the form of an additional, second opening force, wherein this second opening force can be relatively small and is essentially independent of the pressure levels prevailing in the first opening pressure chamber and the first closing pressure chamber. In contrast to the known fuel injection valve mentioned at the beginning, in this instance, a direct actuation or control of the valve member is thus produced. Preferably, the first closing pressure chamber is connected in a virtually unthrottled manner to the high-pressure fuel source. In particular, the first closing pressure chamber can communicate directly with the first opening pressure chamber.
These measures assure that the pressures in the first closing pressure chamber and in the first opening pressure chamber remain constant or behave in virtually the same manner so that the static pressure equilibrium always prevails against the valve member.
In a preferred embodiment of the fuel injection valve according to the invention, the actuation means can have a pressure generator which can adjust a working pressure in a second opening pressure chamber in order to open the valve member. In addition, the valve member can then have a second opening surface which defines the second opening pressure chamber in the opening direction of the valve member, wherein the working pressure in the second opening pressure chamber produces the second opening force against the second opening surface. This kind of hydraulic force transmission is particularly easy to produce and permits a relatively abrasion-free actuation of the valve member. Preferably, the above-mentioned pressure generator drives a piston which defines a working pressure chamber that communicates with the second opening pressure chamber. In this manner, for example, a hydraulic transmission can easily be produced. For example, if a piezoelectric actuator is used as the pressure generator, a relatively small stroke of the piezoelectric actuator can be converted into a relatively large stroke of the valve member by means of this hydraulic transmission.
So that the actuating means only has to produce an opening force and no closing force in order to move the valve member, the first closing force can preferably be selected so that it is slightly greater than the first opening force so that the valve member automatically closes in the absence of a second opening force. Likewise, additional spring means can be provided which drive the valve member into its closed position.
In a preferred embodiment, the first closing pressure chamber can be embodied at an axial end of the valve member remote from the fuel outlet opening, which produces a particularly simple design.
In order to control the fuel outlet opening, the valve member is provided with a sealing zone which cooperates with a corresponding sealing seat. When the valve member opens, this sealing zone lifts up from the valve seat so that the high fuel pressure prevailing against the valve member can act in the opening direction against this sealing zone as well, and against the entire axial end of the valve member oriented toward the fuel outlet opening. As a result, the valve member experiences an additional force in the opening direction which can affect the dynamic opening behavior of the valve member. This property makes it more difficult to meter small fuel injection quantities in which a rapid and reliable closing of the valve member must be produced, particularly before its arrival at an upper or open end position of the valve member. In order to balance this additional opening force during the opening of the valve member, in the fuel injection valve according to the invention, the valve member can have a second closing surface which defines a second closing pressure chamber in the closing direction of the valve member, wherein the pressure in the second closing pressure chamber produces a second closing force against the second closing surface. In addition, a compensation piston can then be provided which on the one hand, defines a compensation pressure chamber that communicates with the second closing pressure chamber, and on the other hand, defines a reference pressure chamber. A pressure increase produced in the second closing pressure chamber by an opening movement of the valve member is limited by the pressure in the reference pressure chamber, which is preferably connected to the high-pressure fuel source, and with a continuing opening motion of the valve member. The pressure in the second closing pressure chamber remains essentially constant as a result of a corresponding adjustment of the compensation piston. In this embodiment, even with the first opening movement of the valve member, a pressure can build up in the second closing pressure chamber which increases very rapidly to a maximum value. Then the pressure remains constant since the position of the compensation piston can change after a particular pressure and as a result, the total volume in the compensation pressure chamber and in the second closing pressure chamber remains constant.
In an advantageous improvement of the above-mentioned embodiment, the compensation pressure chamber and the second closing pressure chamber can be connected via a check valve to a fuel supply. The check valve is oriented so that the check valve opens when there is negative pressure in the compensation pressure chamber and in the second closing pressure chamber and closes when there is excess pressure in the compensation pressure chamber and in the second closing pressure chamber. This additional measure can compensate for leakage losses which can preferably be produced when the valve member is opened and the pressure compensation takes place via the second closing pressure chamber and the compensation pressure chamber.
According to a particularly advantageous embodiment, a fuel network can be provided which has a fuel pressure source whose pressure is greater than the ambient pressure and less than the pressure of the high-pressure fuel source. This fuel network has at least one pressure chamber, which is disposed against an axially adjustable element of the fuel injection valve, axially between a high-pressure region embodied against this element and a low-pressure region embodied against this element. This measure considerably reduces the pressure differential between the respective high-pressure region and low-pressure region by constituting a series of stages. In this connection, the pressure differential between the high-pressure region and the pressure chamber constitutes a first stage and the pressure differential between the pressure chamber and the low-pressure region constitutes a second stage. This results in the fact that considerably smaller leaks occur. At the pressures and adjusting speeds that occur in a fuel injection valve, leaks can trigger cavitations, which lead to damage to the valve member or to the fuel injection valve.
Other important features and advantages of the fuel injection valve according to the invention ensue from the claims, the drawing, and the accompanying Fig. description in conjunction with the drawing.